[Spatial Differentiation and Influencing Factor Analysis of Soil Heavy Metal Content at Town Level Based on Geographic Detector].

Geographic detectors can quickly detect spatial stratified heterogeneity and quantitatively reveal the intensity of driving factors of heavy metal content, which is of great significance for the prevention, control, and remediation of soil heavy metal pollution. In order to reveal the spatial differentiation and influencing factors of soil heavy metal content on the town-scale, 788 topsoil samples were collected from a town in the hinterland of Chengdu Plain. Soil heavy metal (Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni) pollution risk assessments were carried out by using the geo-accumulation index method. Additionally, based on the geographic detector model, 15 factors such as soil properties, topography, soil forming factors, and distance were taken as independent variables, and the contents of each heavy metal element were taken as dependent variables to explore the spatial differentiation and influencing factors of heavy metal content in soils. The results showed that:the average contents of Hg, As, Pb, Cr, Cu, Ni, and Zn in the study area were 1.06-1.93 times the background value of Chengdu, and the content of Cd was lower than the background value; among them, Hg reached the light pollution level, and the other seven heavy metals were at the non-pollution level. The spatial distribution of eight heavy metals was significantly different, the correlation among the elements was significant, and a significant correlation was found between most heavy meals with soil properties; however, the correlation with distance factor and topographic factor was relatively weak. The factor detection showed that TP, TK, pH, TOC, elevation, and distance from the railway had the most significant explanatory power for the heavy metal contents. Interaction detection showed that the interaction between soil properties and other factors was the dominant factor for the spatial variation in heavy metals, and elevation, distance from residential area, distance from railways, and distance from industrial areas were also important factors. Risk detection showed that Hg had the most significant difference in the subregion of elevation and distance from railway, whereas the other seven heavy metals had the most significant difference in the sub-regions of influencing factors of soil properties. The spatial distribution of heavy metals varied significantly in soil at the town-scale, which was closely related to soil properties, topography, and human activities in the study area.

Construction and identification of an infectious clone for CDV-3 strain of canine distemper virus / 生物工程学报

In order to establish an infectious clone for CDV-3, a commercial vaccine strain of canine distemper virus for mink, to provide reference for the studies of pathogenesis and novel vaccine development of CDV. Thirteen pairs of primers were used to amplify the full-length genome of CDV-3 strain. Five long fragments were obtained based on single restriction site analysis of the whole genome of CDV-3 by RT-PCR. Five fragments were successively inserted into the multiple clone sites in the modified eukaryotic vector of pcDNA3.2 by restriction enzymes and splicing. Meanwhile, the hammerhead ribozyme and hepatitis delta virus ribozyme sequences were added to the beginning of F1 fragment and the ending of F5 fragment, respectively. Then, the full-length cDNA recombinant plasmid of CDV-3 was obtained and named as pcDNA3.2-CDV-3. In addition, three helper plasmids, expressing the N protein, P protein and L protein of the CDV-3 strain respectively, were constructed. The 293T cells were transfected with the full-length cDNA recombinant plasmid and three helper plasmids by Lipofectamine™ 2000. At 3 days post transfection, the supernatant was added to the monolayer of Vero cells to observe the typical syncytium of CDV. Indirect immunofluorescence and artificial label identification of recombinant virus rCDV-3 were conducted after the occurrence of lesions. Finally, the growth characteristics of wtCDV-3 and rCDV-3 were compared after passaging of rCDV-3. The identification of the full-length cDNA recombinant plasmid and three helper plasmids by restriction enzyme digestion and sequencing were consistent with expected. The Vero cells infected with the recombinant rCDV-3 showed typical syncytic. The identification of indirect immunofluorescence and labeled marker, and observation under electron microscope proved that the rCDV-3 was indeed rescued from the recombinant plasmid of pcDNA3.2-CDV-3. In comparison of the virus titers of wtCDV-3, rCDV-3 replicated massively and rapidly and reached the maximize virus titer of 10⁷·⁶⁶⁷ TCID₅₀/mL within 36 h post infection (p.i.) in Vero cells, while wtCDV-3 grew gradually to 10⁶·⁶⁶⁷ TCID₅₀/mL at 72 h p.i. in Vero cells. This reverse genetic system of CDV-3 strain has been established successfully, to provide reference for the studies of pathogenesis and novel vaccine development of CDV.